Generally, acoustic transducers convert received electrical signals to acoustic signals when operating in a transmit mode, and/or convert received acoustic signals to electrical signals when operating in a receive mode. The functional relationship between the electrical and acoustic signals of an acoustic transducer depends, in part, on the acoustic transducer's operating parameters, such as natural or resonant frequency, acoustic receive sensitivity, acoustic transmit output power and the like.
Acoustic transducers are manufactured pursuant to specifications that provide specific criteria for the various operating parameters. Applications relying on acoustic transducers, such as piezoelectric ultrasonic transducers and electro-mechanical system (MEMS) transducers, for example, typically require precise conformance with these criteria. Furthermore, these operating parameters are subject to change due to contamination, humidity, temperature and other environmental factors.
In the past, some acoustic devices have been manufactured with processes where the acoustic transducer element is placed in a metal, ceramic, or plastic package and a lid is bonded to the package. With these techniques, a device has to be first cut or otherwise separated from the rest of the wafer before it could be packaged. However, this is relatively costly and results in a packaged part with a relatively large size.
Some newer semiconductor packaging techniques employ wafer-level packaging techniques wherein packaging is performed while the device remains with its wafer. In this fashion, hundreds or thousands of packaged devices can be created simultaneously, and then separated by sawing or other means.
However, these wafer-level packaging techniques can have problems when applied to acoustic transducer devices. The sawing process can generate contaminant particles. The device may also be exposed to moisture and high heat in known these wafer-level packaging techniques that can affect the reliability and operating parameters of the device.
U.S. Pat. No. 6,265,246 discloses a wafer-level package and packaging method that provide a hermetic seal without high voltages or high temperatures. However, in general, a hermetically sealed package is not well—suited to an acoustic transducer where it is desired to communicate an acoustic wave or signal between the acoustic transducer and the external environment.